In the semiconductor field it is common to sequentially grow several different layers of semiconductor material and use various masks and etching steps to form the desired devices and terminals on the devices. In some methods, masking material, e.g. nitride/oxide or the like, is applied and semiconductor material is grown over masked and unmasked areas. The material on the masked areas is then removed by etching and lift-off. In some instances material is selectively grown in unmasked areas and the masking material is then removed. In some processes a photoresist mask is used to define and develop a hard mask, i.e. a metal mask, a nitride mask, etc.
Generally, in these prior art methods of fabricating semiconductor devices, etching is required to remove unwanted material and masks are removed by etching, solvent, or the like. During the etching and/or mask removal processes, the material of the semiconductor device has a high likelihood of being contaminated by the etchant, which contamination greatly reduces the life of the device, the operating characteristics of the device, and the reliability of the device. Further, the etching process severely damages semiconductor material adjacent the etched areas which further reduces life, operating characteristics, and reliability. Also, etching processes are very time consuming and difficult to perform.
Thus, these prior art techniques involve many process steps such as resist spinning, exposure, developing, cleaning and so on. All of these processes can introduce contamination, decrease yield, etc. A further problem that arises is that the structure or substrate (generally a wafer) must be removed from the growth chamber to remove the masking material. The structure is then masked again and reintroduced into the growth chamber for re-growth. Thus, the prior art techniques keep the wafer vacuum incompatible.
In addition to the masking and etching problems, all known prior art fabrication processes require many interspersed growing, masking and etching steps which greatly complicate and lengthen the process. For example, when epitaxial layers are grown, the wafers must be placed in a vacuum or pressure chamber to provide the atmosphere for the growth. Each time the wafer must be etched and/or masked, it must be removed from the chamber, resulting in large amounts of preparation time for each step. Also, each time wafers are removed from a chamber and subsequently replaced, the opening and preparation of the chamber (as well as the processing of the wafer) is an opportunity for additional impurities and contaminants to be introduced to the wafer.
Accordingly, it would be highly desirable to provide fabrication methods for semiconductor devices with improved masking processes.
It is a purpose of the present invention to provide a new and improved method of masking gallium arsenide substrates during semiconductor device fabrication.
It is another purpose of the present invention to provide a new and improved method of masking gallium arsenide substrates during the fabrication of semiconductor devices which does not require removal of the substrate from the processing chamber to remove the mask.
It is still another purpose of the present invention to provide a new and improved method of masking gallium arsenide substrates during the fabrication of semiconductor devices which does not require the introduction of contaminants, such as photoresist, solvents and etchants.
It is a further purpose of the present invention to provide a new and improved method of masking gallium arsenide substrates during the fabrication of semiconductor devices which is much simpler and includes less chance of contamination of the devices.
And a further purpose of the present invention is to reduce the temperature to which the substrate is exposed, to perform the masking steps.
Another purpose of the present invention is to provide a new and improved method of masking gallium arsenide substrates wherein the mask is removed at conditions similar to growth, with small changes in chemistry.
Still another purpose of the present invention is to provide a new and improved method of masking gallium arsenide substrates wherein the mask is removed, enabling regrowth, without significantly etching or contaminating the grown epilayer.
Yet another purpose of the present invention is to provide a new and improved method of masking gallium arsenide substrates enabling the mask to be without changing the gases used for regrowth.